The present invention relates to artificial hair for implantation which is suitable for direct implantation into the skin of a living human body, and a process for producing the artificial hair.
Many kinds of artificial hair for implantation directly into skin of a human body have been proposed. Among these kinds of artificial hair, those which have found practical acceptance include artificial hair with a loop-shaped root part, which is developed by the present inventor and is disclosed in Japanese Patent Publication No. H03-8770 and U.S. Pat. No. 4,793,368. On the basis of the invention disclosed in the above-mentioned patent documents, a monofilament of polyethylene terephthalate (PET) fiber is most desirably employed in this type of artificial hair.
Polyethylene terephthalate fiber has proven to be very safe for human implantation since it is subjected to melt spinning without using an organic solvent, and it also has excellent strength and durability. As a consequence, polyethylene terephthalate has been believed to be the most suitable material for artificial hair.
However, it has been found that, when artificial hair made of polyethylene terephthalate fiber is actually implanted and used for long periods of time, many strands break at points in the vicinity of the roots and fall off. Therefore, in order to solve this problem, the present inventor carried out a test of repeated 180 degree bending at the same place of a single polyethylene terephthalate fiber (i.e., bending fatigue test), and determined that a monofilament having a diameter of 91 xcexcm breaks after it has been bent in this manner about 50,000 times.
In addition, there is another problem that the artificial hair strands fall off due to suppuration at root parts of the artificial hair caused by infection with bacteria during their implantation, thus causing deterioration in the fixation rate of the implanted artificial hair. As a countermeasure to this problem, a method of attaching amorphous silver in spots to the surface of the artificial hair so as to prevent infection due to bacteria during the implantation operation and prevent suppuration due to the bacteria after implantation has been proposed, as disclosed in Japanese Patent Publication No. H04-48460 and U.S. Pat. No. 5,005,596.
However, the method of attaching amorphous silver in spots to the surface of the artificial hair needs complicated and expensive apparatus and, in addition, there is a problem that the vacuum deposition conditions are difficult to control for achieving uniform adherence of the amorphous silver to the surface of the artificial hair.
In order to solve the above-mentioned problems, the present invention provides artificial hair for implantation, which has a high fixation rate of implanted artificial hair strands and high durability such that the artificial hair strands do not break at a root part even after having been used for long periods of time after implantation.
The present invention further provides artificial hair for implantation, which has a low bacterial infection rate, a high fixation rate of implanted artificial hair and high durability such that the artificial hair does not break at a root part even after having been used for long periods of time after implantation.
Further, the present invention provides a process for producing, at a low cost and with simple operations, artificial hair for implantation, which has a high fixation rate of implanted artificial hairs and high durability such that the artificial hair does not break at a root part even after having been used for long periods of time after implantation.
Furthermore, the present invention provides a process for producing, at a low cost and with simple operations, artificial hair for implantation, which has a low bacterial infection rate, a high fixation rate of implanted artificial hairs, and high durability such that the artificial hair does not break at a root part even after having been used for long periods of time after implantation.
As the result of intensive research carried out by the present inventor in order to achieve the above-mentioned objects, artificial hair using a fiber comprising polybutylene terephthalate as its principal component has proven to successfully attain the foregoing objects.
Specifically, an artificial hair strand according to the present invention is characterized in that it is made of a monofilament of a fiber comprising as a principal component polybutylene terephthalate (PBT). Polybutylene terephthalate is known and has been used to make paint brush bristles. It is obtained from direct polycondensation between a terephthalic acid and 1,4-butanediol; or from polycondensation by transesterification between dimethyl terephthalate and 1,4-butanediol. Polyethylene terephthalate is often used for films and fibers, whereas polybutylene terephthalate has been principally used to make molded products. The PBT used inn the practice of the present invention is preferably a compound having a number average molecular weight of 10,000 to 60,000, and preferably 20,000 to 40,000.
Polybutylene terephthalate fiber is usually fabricated by subjecting a polybutylene terephthalate masterbath to melt spinning. In order to produce the artificial hair, the fiber is subjected to a drawing treatment so as to obtain monofilaments having a diameter within a range of 80 xcexcm to 110 xcexcm, and preferably 90 xcexcm to 100 xcexcm. Depending on various applications, pigments may be added to the raw material before the spinning so as to color the artificial hair suitably into black, brown, gray or other colors. The pigments used in the artificial hair are preferably present in an amount less than 3% by weight and are typically carbon black, iron oxide, titanium oxide, or the like. The pigments can be used singly or in the form of a mixture. A root part is formed at one end of the obtained monofilament, for example as disclosed in the first patent documents cited above, and thus the artificial hair is produced.
Artificial hair made of monofilaments of polybutylene terephthalate has substantially the same tensile strength, chemical resistance, light resistance and other properties as those of artificial hair made of monofilaments of polyethylene terephthalate. On the other hand, artificial hair made of monofilaments of polybutylene terephthalate has extremely greater bending fatigue-resistant strength (i.e., the durability in a bending fatigue test) than artificial hair made of monofilaments of polyethylene terephthalate.
Specifically, results of a bending test in which monofilaments are bent repeatedly through 180 degrees at the same place until the monofilament is broken reveal that polyethylene terephthalate fiber breaks after having been bent about 50,000 times, while polybutylene terephthalate fiber does not break even when the number of times of bending reaches 1,500,000. This physical property of polybutylene terephthalate fiber is extremely effective in improving the durability of the artificial hair after implantation.
However, compared to polyethylene terephthalate fiber, polybutylene terephthalate fiber has extremely low lateral stiffness. As a consequence, artificial hair made of polybutylene terephthalate fiber would normally be too soft and therefore would stick to the scalp in an undesired manner.
In order to improve the stiffness of polybutylene terephthalate fiber, the present inventor has ascertained that incorporation into the fiber of a powder of silver ceramics can attain the best results in increasing lateral stiffness without significant diminution of other properties.
Specifically, artificial hair for implantation according to the present invention is characterized by being made of a monofilament of a fiber comprising a principal component of polybutylene terephthalate containing powder of silver ceramics. The silver ceramics used in the present invention include, for example, silver zeolite, silver apatite, silver phosphoric acid calcium, silver phosphoric acid zirconium, and so on. Generally, such silver ceramics may be produced by an ion-exchange reaction between a ceramic and silver ions.